Amazon.com lists an astounding number of dieting books—more than 16,000. But parenting guides far exceed that number: there are some 40,000 of them, including books such as Jane Rankin’s Parenting Experts, that do nothing but evaluate the often conflicting advice the experts offer. People, it seems, are even more nervous about their parenting than they are about their waistlines.

Why is there such chaos and doubt when it comes to parenting? Why, in fact, do most parents continue to parent pretty much the way their own parents did—or, if they disliked the way they were raised, the exact opposite way? Shouldn’t we all just find out what the studies say and parent accordingly?